Miniature Radiogram Replica

I was asked to have a look at a mid-century Murphy 8108 radiogram. It comprised a chassis similar to a Bush SRG1041 and a Garrard 6-300 automatic record changer, and was built in 1970. Unfortunately it was deemed beyond repair. The record changer drive idler (a rubber wheel that drives the platter) had failed. Plastics in the record changer were crumbling, as were the plastics supporting the buttons. Every potentiometer in the amp had failed, the speaker cones were disintegrating and unobtainable transistors were dead. But when I learned of its sentimental value to the owner, something had to be done to keep it alive.

Radiogram Front View Finished

The original cabinet was constructed of veneered chipboard, glued, screwed and stabled together. The speaker grilles were strips of veneered board glued to a hardboard backing, with a layer of cloth separating them from a plywood baffle to which the speaker was mounted. Getting this cabinet to yield its material in a neat fashion wasn’t going to happen, so a few plunge cuts with a jigsaw separated the panels which could then be machined into straight sheet material.

The intent was to produce a miniature replica of the original design, including the original joinery. The top and base panels were rebated to meat the sides, and the front is machined to slot into rebates in the top, bottom and side panels for additional strength. I took some artistic license with a 14 mm rebated back panel and the top, which was assembled in layers, with a panel machined to house the electronics beneath the hinged lid as per the original design.

Radiogram Left End

The primary challenge was working with the old material. I wanted to keep the original veneer but it had other ideas. Some panels were produced several times before I managed to make a full set with minimal veneer damage. Routing the control recess in the top was also a challenge as the old chipboard would crumble to a powdery dust under a chisel or blade. Success was eventually achieved using a router with a new, sharp cutter, following a template in multiple passes of around 0.5 mm. This removed the material and left a smooth finish to be painted, but wasn’t harsh enough to tear the surface. The rebates and housing grooves were machined using a table-mounted trim router with a spiral cutter. Trim routers are designed for smaller cutters and can run at much higher speeds than the much more powerful 3/4HP router usually fitted to the table. In this case the higher speed meant a cleaner cut.

Radiogram Right End

I couldn’t machine the front panel with a router as the veneer was simply too fragile. I used an 84 tooth blade in the table saw to cut the grille slots, carefully stacking spacer plates to achieve an even gap between each slot. Leftover chipboard from the cabinet made perfect speaker baffles. I glued black speaker grille cloth to them, and in turn glued them to the front panel after the gaps between the grilles were painted black to match the original grille design.

Radiogram Rear

The next obstacle was edging the pieces. I decided at the onset that I wouldn’t use any additional material other than what could be salvaged from the original cabinet. So I cut some strips from the leftover panels and used a wide blade in the bandsaw to remove the veneer from the surfaces. The veneer had been bonded for nearly 55 years and the instability in the old material left an uneven cut with some of the original chipboard left behind.

Radiogram Inside View Overall

I resorted to sticking the strips face down to a piece of scrap board and sanding their back faces with an orbital sander and 60, 80 and 120-grit discs to produce clean, flat bonding surfaces. The boards were edged by gluing the veneers in place and clamping them in a bench vice between flat scraps of laminated board. When they were dry I trimmed the excess with a block plane and a chisel. Some of the veneer edges chipped during the trimming process, so I’d have to cut them off and start again. I went through a lot of veneer, but eventually achieved veneered edges with minimal defects.

Radiogram Top Lid Shut

Once the cabinet was assembled the few surface chips and edge seams were blended with a two-part wood filler. The cabinet was sanded at 80 grit before 120, 180 and eventually 240 to achieve the final finish. This was a delicate process as it was necessary to remove the original wax polish and varnish finish to apply a new stain, but the slightest over sand would break through the veneer. At this point the veneer was at its most fragile. Just moving the cabinet was enough to put a dig in the surface.

The lid was installed using a piece of the original piano hinge, cleaned up with some polishing compound and wax. I replicated the original lid support block, which provides a 15-degree back-tilt when the lid is lifted.

Radiogram Lid Up Resting On Bracket

The plinth and tapered legs are close replicas of the originals. The originals were hardwood (presumably Sapele) and I reused those pieces to create the miniature replicas. The plinth also serves as a handy space to add the original model plates, cut from the back of the original cabinet.

Radiogram Underside Label

The finish is a medium oak tinted wax. Several coats of this blended any variances in the veneer and the filler and built up a protective layer that partially soaked into the wood. Once it had dried for a day or two, I applied several coats of microcrystalline wax and buffed to achieve the final finish. The microcrystalline forms a hard-wearing surface that resists moisture, finger marks and physical damage. It’s one of the best ways to protect old wood and can be applied over almost any finish and to most materials.

I wanted this to be a useful item, not just a decorative one. It has inbuilt Bluetooth 5.0, USB and SD card support, a line input socket (for a turntable, perhaps), a remote control and an FM radio. This is all based around a minimal circuit comprising a couple of chips, the same used in a lot of Bluetooth speakers. These do have their limitations, including speech prompts pre-programmed into the microcontroller that can’t be disabled, but they work well and have decent sound quality.

Radiogram Close Up Of Inside

The amplifier uses a PAM8403 class D chip with 3 watts per channel – the same output power as the original radiogram. I love these amps as they’re tiny, require only a few surface-mounted supporting components which fit neatly on the same board and they sound great. The 2 3 inch speakers were removed from a scrap boombox a few years ago. The power supply is a 3 amp switching unit with overload, overvoltage, overtemperature and short circuit protection. It’s vintage meets modern, and it worked really well.

Radiogram Top Lid Up

The result is a reasonably accurate replica of the original radiogram cabinet. It is almost quarter scale though not exactly. I calculated the enclosure based on some measurements taken from the speakers. It sounds surprisingly good for such a small unit, on a par with a typical tabletop radio. It was a challenging project to overcome the shortcomings of the aging materials and produce an authentic replica. The result, I think, is one of my best builds to date.

Radiogram Top View With Remote

Join The Discussion

Discover more from The Blind Man's Workshop

Subscribe now to keep reading and get access to the full archive.

Continue reading